We propose to examine the mechanisms which underlie the perception and voluntary control of lung volume changes. These will include the role of chest and/or abdomen position, rate of change of lung volume (flow) and force or effort exerted by respiratory muscles. Subjective cues which individuals use to detect lung volume changes will be examined since they may provide further insight into physiological mechanisms. In addition we will measure the threshold for respiratory load detection during rest and exercise to ascertain whether load detection is more sensitive during exercise than at rest. Standard psychophysiological procedures (Method of Adjustment, Method of Constant Stimuli, Method of Limits) will be used to determine the threshold and/or sensitiviy for volume perception and load detection. The relationships between respiratory chemosensitivity, load detection threshold, and volume perception will be studied. The effect of various respiratory stimuli (exercise, increased dead space, respiratory loads) on the breathing patterns will be examined to determine if subjects learn to respond to a particular stimulus in the way which is most appropriate for both gas exchange and efficiency of respiratory work.